DETERMINATION OF THE CYTOPROTECTIVE AGENT WR-2721 (AMIFOSTINE, ETHYOL(R)) AND ITS METABOLITES IN HUMAN BLOOD USING MONOBROMOBIMANE FLUORESCENT LABELING AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Purpose: WR-2721 [S-3-(3-aminopropylamino)ethylphosphorothioic acid] i s a chemoprotective agent that is currently in pediatric clinical tria ls. It is a prodrug that is dephosphorylated by alkaline phosphatase t o the active free thiol form, WR-1065 [S-2-(3-aminopropylamino)ethanet hiol]. It is likely that adequate and sustained cellular levels of the drug are necessary for optimum cytoprotection. To date, a method to m easure both plasma and cellular levels of WR-2721 and its metabolites in clinical samples has not been available. Methods: In the study repo rted here the monobromobimane (mBBr) fluorescent labeling method nias used to measure these levels when drug was added in vitro to blood sam ples from normal volunteers. Tn addition, we present pharmacokinetic d ata from a pediatric patient receiving WR-2721 (825 mg/m(2) x 2). Resu lts: The results can be summarized as follows: (1) WR-2721 was detecte d in the patient's plasma with a half-life of about 10 min; (3) the WR -1065 concentration in the blood cellular fraction was similar to that of plasma, (3) both WR-1065 and WR-SS-low molecular weight (WR-SS-LMW ) metabolites disappeared from plasma and the cellular fraction by 3.6 h after WR-2721 infusion; (4) a large proportion of WR-1065 was oxidi zed in plasma to WR-SS protein and WR-SS-LMW; (5) a large proportion o f WR-1065 in the cellular fraction was oxidized to WR-SS-protein; (6) the WR-SS-LMW concentration in the cellular fraction was low, and (7) saturation of plasma and cellular protein binding sites was possible. Conclusions: The pharmacokinetic data that were generated with this te chnique could guide clinical trials using WR-2721.